I have a set of CNC ported 6.1L heads that came off a car I parted out about 4 years ago. I had then cleaned up and inspected by my machine shop. They did a valve job and installed new valve seals.
While the heads were off, I removed the lifters and installed an Arrington SR2B camshaft. With a good tune, the CNC ported heads and cam should be good for close to 500hp